James olds and peter milner (1954) were trying to implant an electrode in a rat's reticular formation when they mistakenly placed the electrode incorrectly. curiously, as if seeking more stimulation, the rat kept returning to the location where it had been when it received a stimulus from this misplaced electrode. on discovering that they had actually placed the device in a region of the _____, olds and milner realized they had stumbled upon a _____.